Hi,
I am sorry I did not attend the conference, I thought it will be Q3
only solution.
I have one comment. In H.323 we have different conferences models,
centralised or distributed, unlike the centralised model of the H.320.
I think that in the goals and proposal we should define how FECC works
in distributed conferences.
Roni Even
Accord
email: roni_e(a)accord.co.il
______________________________ Reply Separator _________________________________
Subject: PictureTel Proposal for H.323 Remote Device Control
Author: <ITU-SG16(a)MAILBAG.INTEL.COM> at internet
Date: 5/8/98 2:50 PM
This is a summary of the PictureTel proposal for Remote Device Control for
H.323, which we discussed in the Q3/Q14 audio conference held on May 7.
The Goals:
1) Provide FECC for H.323 conferences.
2) Interoperate with H.320 and H.324 systems with H.281 through gateways.
3) Simple to implement for basic FECC model using H.281 compatible
messages. Additional features should be optional.
4) Use a common protocol for point-to-point and multipoint conferences.
5) Add optional support for new camera control mechanisms and for control
of other types of devices, such as in T.RDC.
6) Make it extensible for new standard and non-standard features.
The Proposal:
1) Start by encapsulating the whole H.224/H.281 stack within UDP, in an
H.245 logical channel.
2) Add timestamps to real-time (start/continue/stop) messages, somehow (RTP
or other). Receivers can use this to compensate for jitter in the network.
Receivers free to ignore these.
3) Add functions from T.RDC into H.281 as optional extensions. Probably we
will want to modify these a little, for instance to support positioning
units based on field of view. One possibility is to define a new H.281
command code which indicates the rest of the PDU is an ASN.1 coded message,
and use the ASN.1 taken from T.RDC.
4) For non-real-time commands (all except start/continue/stop), add a
simple retransmission mechanism (just numbered messages and numbered ACKs)
to supply reliable (if inefficient) transport on top of UDP. We can crib
this from existing standards, such as NSRP from Annex A/H.324.
5) Define the functions of an H.224 router to reside in an MC or MCU. This
would mostly be to manage flow control (or not) as does the H.320 LSD
channel, rebroadcast info, route info, etc. This might also include
caching capsets.
6) Make sure addressing and scope issues are synchronized with H.245 (use
M/T addressing probably).
7) Break out the capability exchange function of H.224 into a new H.245
(and therefore TCP) generic cap exchange function that doesn't require the
H.245 engine to recognize the contents of the caps, but merely to pass them
along (as does H.224 capex). These "non collapsing capabilities" will map
1:1 at the gateway to the existing H.224 cap exchange.
8) In future, add T.124-like capability collapsing (AND, OR, etc.) to
H.245. Details need work, but we'd like to support multicast and large
conferences. This is not immediately useful for RDC, but would supply a
generic extended H.224 stack that would provide for future simple control
protocols without requiring upgrades to deployed infrastructure equipment
such as MCs, MCUs, and gateways.
Mark Duckworth
PictureTel
duckworthm(a)pictel.com
